Add the nss/lib/pkcs12 directory from NSS (Mozilla's Network Security Services) to third_party. Th…

nss_pkcs12/README

Index: nss_pkcs12/README
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--- nss_pkcs12/README	(revision 0)
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+Name: Network Security Services (NSS) pkcs12 directory
+Short Name: nss_pkcs12
+URL: http://www.mozilla.org/projects/security/pki/nss/
+Version: 3.15.1
+License: MPL 2
+License File: COPYING
+
+Description:
+This is a copy of the directory nss/lib/pkcs12 from the NSS open-source
+secure networking library. Dart gets the rest of NSS from Chromium's
+modified copy of NSS, but Chromium's version omits this directory.
+
+This has been copied from a downloaded copy of NSS, rather than checked out
+from the original repository. No changes or patches have been made to it.
+This directory should be updated manually whenever the version of NSS in
+Dart's checkout of third_party/nss from Chromium is updated.
+
+The file COPYING has been copied from nss/COPYING in the original.